Physics 101: Why Did the Universe Blow Up?

Gravitational waves from inflation generate a twisting pattern in the polarization of the cosmic microwave background. Shown here is the actual pattern observed with the BICEP2 telescope.

Credit The BICEP2 Collaboration

Recent observations of so-called "gravitational waves" are providing astronomers with the strongest confirmation yet of cosmic inflation, a theory that says the universe rapidly expanded following the Big Bang.

Why, exactly, did the universe balloon by 100 trillion trillion times, in less than the blink of an eye, 13.8 billion years ago?

For the answer to that, I called up Seth Redfield, assistant professor of astronomy at Wesleyan University. Redfield said that long ago, the universe’s four fundamental forces — gravity, electromagnetism and the strong and weak forces — may have been united in one big cosmic stew. "Early in the universe," he said, "as you crank up the temperature of matter, these forces unite and they become indistinguishable from each other."

The sun sets behind BICEP2 (in the foreground) and the South Pole Telescope (in the background). This month, BICEP2 discovered the first direct evidence of cosmic inflation.

Credit Steffen Richter (Harvard University)

They were indistinguishable, but full of a lot of latent energy. As the universe began to cool, parts of that stew separated out. "Assuming these forces are all united in this very first instant of the Big Bang," Redfield said, "as it cools, these forces will ‘freeze’ out, so to speak. They will start to distinguish themselves from each other."

At a certain point, gravity froze out. Then the strong force followed suit, followed by electromagnetic and weak. Each time a force was kicked out of the cosmic stew, latent energy was released.

Redfield said that energy fueled the cosmic expansion, with each separation acting as an injection of energy that inflated a single point to an entire universe in an instant.

A brief history of cosmic time.

Credit BICEP2 Collaboration

"One of the things inflation helps us understand is why the universe looks so homogenous," Redfield said. "We look in different parts of the universe and we see that it’s about the same temperature so we need this extreme inflation, that takes something that’s really small and then expands it into this much larger size."

As time marches on, some scientists believe that yet undiscovered forces could still differentiate themselves from the cosmic stew, further altering the very fabric of the cosmos. "Perhaps the phase transitions aren't done," Redfield said. "This is tied up with one of the most exciting new discoveries over the last 20 years and that's dark energy ... it's possible that there could be phase changes in the future that would alter the structure of dark energy ... who knows, at this point. And this is why this is so much fun to think about."